1. Field of the Invention
The present invention relates to a bonding wire inspection apparatus that automatically inspects the condition of wires bonded between the pads of a semiconductor chip and the leads of a lead frame.
2. Prior Art
FIGS. 6 through 9 show a sample 6 that is an example to be inspected. The sample 6 includes wires 5 that are bonded between the pads 2 of a semiconductor chip 1 and the leads 4 of a lead frame 3. In these Figures, reference numeral 7 refers to squeezed out paste that is used for bonding the semiconductor chip 1 to the lead frame 3. FIG. 5 shows one of the conventional inspection apparatuses.
In this inspection apparatus, a vertical illumination means 11 is located above the sample 6, which is placed on an inspection stand 10. The vertical illumination means 11 is installed at the bottom of an optical means 12, and a CCD camera 13, that consists of a CCD (photoelectric converter element) and a driving source therefor, is mounted on the top of the optical means 12. The CCD outputs an image signal of the image of the sample 6 taken in by the optical means 12. The image signal from the CCD camera 13 is processed by an image-processing arithmetic unit 14. Thus, the shape of the wire 5 is recognized, and the bonded position of the wire 5 is also observed.
The optical means 12, that includes the vertical illumination means 11 and the CCD camera 13, is provided on an X-Y table 15. Inside the vertical illumination means 11, a half-mirror 16 is installed so that the half-mirror 16 is positioned straight beneath the CCD camera 13. Also inside the vertical illumination means 11 are a condensing lens 17 and a light bulb 18 that are installed on one side of the half-mirror 16.
The bonding wire inspection apparatus of this type is described in, for example, Japanese Patent Application Laid-Open (Kokai) No. 3-76137.
In the apparatus shown in FIG. 5, when the vertical illumination means 11 is switched on, the light from the light bulb 18 passes through the condensing lens 17, is reflected by the half-mirror 16, and then vertically directed onto the sample 6. Then, the X-Y table 15 is moved so that the CCD camera 13 is positioned above the object of inspection or the sample 6 that is on the inspection stand 10, and the image signal (that represents microscopic parts of the object of inspection, such as the ball and crescent at both ends of a bonded wire) obtained by the CCD camera 13 is subjected to noise removal, edge enhancement in the inspection area and enlargement or reduction of the image, etc. by means of the image-processing arithmetic unit 14, thus enhancing (restoring) the image of the microscopic parts of the object of inspection so that the image is easier to see. Afterward, the inspection and measurement operations are performed.
When the microscopic parts of the object of inspection are thus optically imaged, the magnification of the optical means 12 is set at a high value. For example, the magnification is set to be 2 to 3 times larger when a 2/3 inch CCD camera is used.
In recent years, semiconductor chips are increased in size, and the dimensions of the area in which the wire bonding is performed are now as large as 30 mm square or thereabouts. Since the microscopic portions, that are to be inspected, are located in such a broad range as 30 mm square area, it is necessary in the prior art to move the vertical illumination means 11 and the optical system 12, which are heavy in weight, great distance. As a result, the size of the X-Y table needs to be large, which makes rapid movement of the illumination means difficult and increases the cost of the inspection apparatus.
In addition, since the vertical illumination means 11 and the optical system 12 which are located above the sample 6 are moved, dirt, etc. would fall onto the sample 6 as the vertical illumination means 11 and the optical system 12 move. In other words, in semiconductor devices which are extremely averse to contamination by dirt, etc., those parts that move above the sample tends to cause various problems and therefore should be avoided, even in the process in which the sample is under inspection.